area of a quadrilateral
Let a,b,c,d be the lengths of the sides of a quadrilateral and K be its area.
Let s be the semiperimeter.
Then
K2=(s-a)(s-b)(s-c)(s-d)-abcdcos2(θ+ϕ2) |
where θ and ϕ are of the quadrilateral. Letting d→0 we obtain Heron’s formula for the area of a triangle.
References
- 1 C.A. Bretschneider, Untersuchung der trigonometrischen Relationen des geradlinigen Viereckes. Archiv der Math. 2, (1842), 225-261.
- 2 F. Strehlke, Zwei neue Sätze vom ebenen und shpärischen Viereck und Umkehrung des Ptolemaischen Lehrsatzes. Archiv der Math. 2, (1842) 323-326.
Title | area of a quadrilateral |
---|---|
Canonical name | AreaOfAQuadrilateral |
Date of creation | 2013-03-22 16:58:22 |
Last modified on | 2013-03-22 16:58:22 |
Owner | Mathprof (13753) |
Last modified by | Mathprof (13753) |
Numerical id | 7 |
Author | Mathprof (13753) |
Entry type | Theorem |
Classification | msc 51N20 |